It is well known that ghosts or echoes are produced in a video signal sequence when the signal is subject to multiple reflections and multi-path propagation. Depending on the path differences between different signals arriving at a receiver, time delays between a main signal and ghosts of the signal can vary between -5 .mu.s and +45 .mu.s. It is known to remove ghost signals in such a video sequence by filtering using an adaptive filter to inverse filter the signal. Such filters operating in the time domain need a very long transversal filter with programmable coefficients. In this way a digital sample of the video signal is multiplied simultaneously by each of the filter coefficients. To remove a ghost signal at a time delay T after the main signal it is necessary for the data sample to have a length T/d where d is the digital sample frequency of the data. In the case of video signals the frequency is such that the length of data sample T/d is sufficiently great that a very long filter is required to handle the multiplication of all the digital values in the sample simultaneously. A suitable filter in the time domain may require something of the order of 600 taps each tap effecting one multiplication. Due to the limitations of hardware techniques in the filters such long filters have been produced by cascading shorter filters with consequent increase in expense. An alternative technique has been to use shorter filters and programmable delay lines. This however limits the number of ghosts that can be cancelled at any one time.